mention 6.d as next release

Author: stmuk

doc/Language/faq.pod6

@@ -21,7 +21,8 @@ of the language with the exact version 6.0.0.
 
 It was first implemented by the Rakudo Perl 6 compiler version 2015.12 and is
 likely to be supported by subsequent releases for the foreseeable future by use
-of the 'use 6.c' pragma.
+of the 'use 6.c' pragma. The next compiler version (no release date) is to be
+v6.d.
 
 =head2 As a Perl 6 beginner what should I install?